The team created the super-strong high endurance creatures by suppressing a natural muscle growth inhibitor. Genome regulator NCoR1 is a molecular brake that decreases activity of certain genes. This brake can be "released" through mutation or using chemicals and this, in turn, reactivates gene circuits to provide more energy to muscle and enhance its activity. This lead to the creation of super mice with muscles that are twice as strong as those of regular mice, even when the muscle was inactive.

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Ronald M Evans, a professor at Salk's Gene Expression Lab, says: "There are now ways to develop drugs for people who are unable to exercise due to obesity or other health complications, such as diabetes, immobility and frailty. We can now engineer specific gene networks in muscle to give the benefits of exercise to sedentary mice."

Researchers experimented with both mice and nematodes, genetically manipulating the offspring of these species to repress NCoR1, the muscle build-up inhibitor. Without the inhibitor, the muscle develops much more effectively.

The muscly mice were able to run faster and longer before showing signs of fatigue. They also exhibited better cold tolerance. Similar results were seen in nematode worms, which let the researchers conclude that their results could be relevant to a range of living creatures.

Under the microscope the muscles could be seen to be bigger, with denser fibres and with cells that had more mitochondria, the cellular organelles that deliver energy to the muscles.

So far the researchers haven't found any harmful side effects associated with eliminating the NCoR1 receptor from muscle and fat tissue, and are now investigating drug molecules that could be used to reduce the receptor's effectiveness.

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Johan Auwerx, the lead author from EPFL, said: "This could be used to combat muscle weakness in the elderly, which leads to falls and contributes to hospitalisations. In addition, we think that this could be used as a basis for developing a treatment for genetic muscular dystrophy."

He added that if these results are confirmed in humans, there's no question they will attract interest from athletes as well as medical experts.